1. Field of the Invention
The invention pertains to the field of silent chains. More particularly, the invention pertains to an improvement in sprocket structure to decrease partial wear on sprocket teeth.
2. Description of Related Art
A silent chain is used as a power transmission chain for automobiles, motorcycles and the like. A silent chain is generally comprised of a plurality of link plates each having a pair of teeth and pin apertures, arranged in lateral and longitudinal directions, and pivotally connected by connecting pins inserted into the pin apertures.
In prior art FIGS. 4 and 5 illustrate an engaging state of a sprocket tooth with a silent chain. As shown in these drawings, a silent chain 1 is comprised of link rows 4 that are formed of a plurality of link plates 2 and guide rows 5 that are disposed adjacent to the link rows 4 and are formed of a plurality of link plates 2 and outermost guide links 3.
A link plate 2 includes a pair of teeth (not shown) that engage with a sprocket tooth 6. Guide links 3 are provided to maintain the silent chain 1 on the sprocket tooth 6 during engagement and does not include a tooth for engagement with a chain.
In order to smoothly engage the silent chain with a sprocket tooth, a distance W between the inside surfaces of the oppositely disposed guide links 3 is greater than a tooth width T of a sprocket. The difference Δ(=W−T) is a clearance of the silent chain 1.
With regard to the engagement of a guide row 5 with sprocket tooth 6, as shown in FIG. 4, an entire surface of each of the link plates 2 of guide row 5 comes into contact with sprocket tooth 6. In FIG. 4, each hatched portion 6A shows a respective engagement surface of each of the link plates 2 on the sprocket tooth 6. Also, one side surface 60 of the sprocket is in close contact with an inside surface of a guide link 3 and a maximum clearance Δ is formed between the other side surface 60 of the sprocket and an inside surface of the other guide link 3.
With regard to the engagement of a link row 4 with sprocket tooth 6, as shown in FIG. 5, all the link plates 2 except the outermost link plate is in whole-surface contact with sprocket tooth 6. The outermost link plate 2 with clearance Δ relative to the sprocket tooth 6 is in a partial-surface contact with the sprocket tooth 6. In FIG. 5, each hatched portion (6A, 6A′) shows a respective engagement surface of each of the link plates 2 on the sprocket tooth 6. The hatched portion 6A is a surface with which a link plate 2 comes into a whole surface contact, whereas the hatched portion 6A′ is a surface with which a link plate 2 comes into partial surface contact.
In this case, during operation of a silent chain, the surface pressure caused by the link plate 2 on the sprocket tooth 6 is highest at the hatched, partial contact surface 6A′, thereby causing a partial wear on the sprocket tooth surface at the hatched portion 6A′. As the partial wear progresses, the surface pressures of the hatched portions 6A caused by the remaining link plates 2 on the sprocket tooth surface increases. As a result, wear to the whole surface of the sprocket tooth progresses.
The present invention has been made in view of these circumstances and its object is to provide a sprocket for a silent chain that can decrease partial wear to the sprocket tooth.